Radio tube



March 16, 1937. H. P. PRATT RADIO TUBE Original Filed Nov. 25, 1928 2Sheets-Sheet l I I I I I IIIIIII'I n 1/6]? tar- March 16, 1937. H. P.PRATT RADIO TUBE Original Filed Nov. 23, 1923 2 Sheets-Sheet 2 W W? W 15W Patented Mar. 16, 1937 PATENT OFFICE RADIO TUBE Harry P. Pratt,Chicago, Ill., assignor to William Frederick Grower, Henry Asa Allen,George Squires Herrington,

and Howard Thompson Ballard, trustees, acting with said Harry I. Pratt,as cotrustees of Pratt Radio Trust Original application November 2s,192s, Serial Divided and this application February, 26, 1934, Serial No.712,876

e iCiaims. My invention relates in general to radio tubes, and relatesmore in particular to a tube designed to be used in place of the presentA. C. type of tube, but so designed that it may be used toreplace anyradio tube as used in the present radio receivers. M

The results obtained in the reception of musi- -cal programs and thelike with the present reeeivers operating on the A. C. principle or D.C.

receivers utilizing A. 0. power packs, is unsatisfactory. There is anunusually large amount of, noise usually referredto as static, althoughI have found that a great deal of this noise is due to interferenceother than strictly static interference. I have found that the presentmethod of plugging in on the commercial electric circuit for eithereliminators or with A. C. tubes is detrimental because itapparentlyconnects the grid circuit within the vacuum tube directly orindi- .20 rectly with the power circuit, thereby causing a short circuitbetween all receiving sets plugged in on the same line, and this notonly cuts down thedistance reception very greatly, but interferes badlywith local reception.

1 methods and equipment, every slight electrical disturbance and everystray electrical vibration picked up by the power line (and there aremany oi these stray currents impressed on every line) is broughtdirectly to the inside of the tube, therebycausingdistortion of thereceived signal as well as the production of noisein accordance with theamount of interference present.

I know that radio engineers are aware of the j existence of at leastsome of these interfering cur- 1 rentsand that'various means areresorted to to filter out these false currents, but this is never donewith any degree of success.

Accordingly, one of the principal objects of my present inventionis theproduction of a radio tube wherein the introduction of these interferingcurrents into the receiver is avoided.

Another object is to provide a tube which does notcome in direct contactwith the power cir- ,45 cuit and yet accemplishes. practically the samedesired results without the many undesirable j traits of thepresent typeof tube.

Another object of the invention is the concentration and retention of aneven heat in the '50 cathode in order to permit continued use of a tubefor a considerable length of time after it is disconnected from a powersource.

In accordance with the main features of my invention I provide two,three, or more, vacuum 55 chambers concentrically arranged and havingthe I have also found that with present standard effect of shielding theheating electrode from the cathode or filament of the tube and at thesame timesealing the greater portion of the heat within the tube toavoid the loss of power through the dissipation of heat. In onemodification of my invention, I provide a relatively large amount ofemitting material which is capable of absorbing 'and retaining more heatenergy in the active portion of the cathode itself. This increased mass,under varying input conditions, maintains a much more even temperatureat the outer surface of the cathode than does the usual arrangement, andthus achieves a more even rate of emission than has heretofore beenobtained, and thus stabilizes tube action. Another feature is theintroduction of a series of thermo couplings which, when once heatedfrom a primary source, will function and keep up the radiating heat fora period of time which saves energy and also saves the C-battery onaccount of the thermocoupling directing the impulses.

Other objects and features of the invention will be apparent from aconsideration of the detail description taken with the accompanyingdrawings, wherein:

Fig. 1 is a vertical central section through a radio tube constructed inaccordance with the main features of my invention;

Fig. 2 is a similar view showing the same features employed in amodified construction;

Fig. 3 is a plan sectional view taken along the line 3-3 of Fig. 1; v V

Fig. 4 is a fragmentary enlarged view showing the construction of theelement as it may be employed in a radio tube for the emission ofmaterial particles, gases, electrons, etc.;

Fig. 5 shows still another modification utilizing "in a slightlydifferent way one of the main features'of the invention;

Fig. 6 is a fragmentary sectional view showing the arrangement of theelements in the embodi ment of Fig. 5; and

Fig. '7 is a greatly enlarged detail showing the construction of one ofthe elements.

Referring first to Fig. 1, the main glass body of the tube comprises anouter wall l0 forming a large chamber ii, an inner wall l2, forming aninner chamber l3, and a third inner wall l4 within the wall l2 andforming a chamber IS in communication with the chamber ll. Within thechamber I 3 and, grouped around the inner tubular glass wall I4, Iarrange the main elements of the tube, including a filament or materialparticle emitting element IT, a grid l8 and a plate element l9. In thisfigure I show all of of glass l0", through which the grid connection 3|.

these elements as coils of suitable wire concentrically arranged abouteach other, but they may have other shapes in accordance with theselection of a manufacturer or peculiarities in the design of the two.Instead of passing electrical current directly through the filamentelement for the purpose of heating it, I prefer, as shown, to supply aheating element 2| arranged within the chamber l6 and designed to beheated from an outside electrical source and furnish its heat to thefilament immediately surrounding it so that emission of suitable currentcarrying particles, usually electrons, will result. In the specificarrangement of this heating element, as shown, I provide a central tube22 which'is of refractory material, and an outside tube 23 formed ofsuitable electrical current insulating and heat transferring material,such as porcelain. The heating element 2| is arranged to neutralizepolarity and decrease interference and directional effect as much aspossible consistent with the space it is to occupy. Good results may besecured by bringing one terminal directly through the tube 22 in themanner shown, bending it up at 24 and carrying the wire by a series ofhelices to the top of the tube for return to its terminal. For formingelectrical contact with the element 2| from an outside source, I provideterminals 26 and 21 which are sealed through an enlarged portion III ofthe outside wall It and Joined in the usual manner to the ends of theresistance element 2|. A suitable protecting cap 28 is provided at thetop of the tube for its protection at this point.

At the bottom of the tube the walls I! and I2 are brought together toform terminals 29, 3|, and 32 are sealed, a protecting cap 33 beingsupplied in the usual manner. These terminals are connected in asuitable way to the elements of the tube within the chamber l3. Inactual practice I show the terminal 32 connected to the filament I! by acontinuation 32 The terminal 3| is connected to the grid 18 by aconnection 3| and to the filament i! by a connection 3|", while theterminal 23 is connected to the plate element i3 by a connection 23'. Inthis way the necessary circuits for the employment of the tube in theusual radio receiver are provided, the plate circuit of the receiverincluding the terminals 29 and 32, while the usual C-circuit makes useof For the evacuation of the tube the usual evacuating passageway 34 isprovided through the glass I 3'', and this is arranged so that theentire tube, including all of the chambers, may be evacuated separatelyor sealed off separately. This, of course, may be modified, but it isquite apparent that with the evacuation of the chamber II the chamber IEwill also be evacuated, as it is in connection therewith.

When this tube is in operation the terminals 26 and 21 are connected toa suitable source of electrical power to heat the element It and thefilamentary element II. This heating element being entirely separatedelectrically, and every way except from a heat transfer point of view,from the other elements, none of the usual interference results. Theevacuated chamber entirely surrounding the other two chambers in whichthe elements are contained, acts as a very good heat insulator to avoidthe transfer of any heat energy through the outer walls of the tube. Toincrease this effect, I may provide a deposit 36 on the inside of thewall III of the tube to an enlarged body act as a mirror as used inordinary Dewar vessels, so that any heat rays striking the outer wallsof the tube will be reflected back and there will be little or notransmission of heat. By bringing the tube up to temperature it can thenbe operated for a considerable length of time without any further energyinput as far as electronic emission from the element I1 is concerned. Byutilizing a suitable switch operating on a thermostatic principle I maymaintain the temperature of the electron emitting element at a high"constant. The current may be oil! the greater portion of the time, butas soon as it drops below a temperature controlled by athermostaticswitch, heating current will be again supplied.

In the arrangement of Fig. 2, substantially the same features areemployed as described in connection with Fig. 1, but I show anadditional feature which will be brought out. In general structure Iprovide-an outer wall I I0, an intermediate wall H2, and an inner wallH. The other portions of the tube are numbered in accordance with thereference characters employed in Fig. 1, except with the numeral I usedas a prefix. In this form all of the terminals are brought through thebase of the tube through the member ||II and the inner chamber 6 isunconnected with the outer chamber Ill. The elements are shown as formedof wire helices, but arecloser together than in the form of Fig. 1. Thefilamentary element H1 is heated by the heating element I2 I, as in thefirst described form, but I imbed as is distinctly shown in Fig. 4 thiselement in a relatively large amount of a material I3l which will havethe triple property of emitting material particles, holding aconsiderable amount of heat, and serving as a path for the transfer ofelectrical energy from the filament to the plate and through the grid,as is done when the tubes are used in radio receivers. Material I3! ispreferably, in this form of the invention, a substance which will emit agas which, at extremely low pressures within the tube, will be ionizedfor ready transfer of current thereover. A material of this character,for example, is sodium, but any substance which will emit particles of anature to carry an electric current when ionized may be used in thisconnection. The arrangement is such that only relatively small amountsof the substance will be emitted on heating of the tube, but when thetube has cooled, the material will again absorb or occlude most of thisgas.

In the arrangement of Fig. 5 I depart somewhat from the first two formsand provide an outer wall 2H! and an inner wall 2| 2, the elements beingdisposed entirely within the chamber 2. A heating coil 22| is employed,being wound in a series of helices about a suitable refractory base 222and having suitable leads 22l' and 22| connecting to the terminals 226and 221. The chamber 2|3 may be filled with a low pressure gas vapor orit may be entirely evacuated so that dependence for the transfer ofelectrical energy from the filament to the grid rests entirely upon thecustomary emission of the electrons from the filaments. The elementswithin the chamber 2l3 are different in form than shown in the otherviews but comprise a filament 2| 1, a pair of grids 2 l8 and plates 2l9. These are connected by suitable connections to terminals 229 sealedthrough the glass bottom 2|ll of the tube. In operation this tube is notsubstantially different than the others.

In Fig. '1 I show a section of an element wherein I employ two cones BIand 52 connected at their apices and formed of diflerent material,preferably of electro-positive and electro-negative metals. I show themconnected for the purpose of 'illustrationby terminals 53 and 54. Ifound that if current is passed through these two cones they will beheated locally at their apices where the cross section is small, whileremaining relatively cool at all other points. While in this condition,a high frequency alternating current may be connected across theterminals, and it will be found that these two cones act as a radiovalve, permitting current to pass only in one direction, the phenomenonbeing similar to that known to exist with the ordinary crystal". Byheating the common apex 56 in any suitable manner I may employ a seriesof these cones as an ele-- ment within a tube and pass the receivedsignal therethrough in order to employ this principle in a detector; oraseries of these cones can be used with an amplifying tube, or, in fact,in any way or under any circumstances in which this principle can beutilized. I may employ these cones opposed in this manner, or a seriesof them in the elements of the tubes shown in Figs. 1, 2, and 5, and soobtain the advantage of the incorporation of these various featurestogether. The cones of Fig. '7 are a great deal larger than cones whichI will employ within a tube, although for certain purposes cones of thismagnitude might be feasible.

This application is a division of an application filed by me November23, 1928, Serial Number 321,347, Radio tube, Patent No. 1,949,395.

While I have described many features of my invention and showndetailedmodifications thereof to enable those skilled in the art to understandand practice the same, I do not restrict myself to the details shown anddescribed, but the invention is limited only by the scope of theappended claims.

What I claim is:

1. In a radio tube a pair of evacuated chambers, one within the other,cathode, grid and plate elements within the inner evacuated chamber, athird chamber of narrow tube-like character extending within the innerchamber, and a heating element disposed within the third chamber forsupplying heat to the elements within the inner chamber.

2. A radio tube including in combination a chamber with the usual radioelements therein, a heating coil disposed in a position to impart heatto the radio element but arranged out of connection with the elementcontaining chamber, and an outer chamber evacuated to form a heatinsulator for the element containing chamber, said heating element lyingwithin said usual radio elements and located within said outer chamber,said outer chamber being out of communication with the inner chamber.

3. A radio tube having three separate vacuum chambers arranged onewithin another, whereof the innermost chamber is provided with a heatingelement, the intermediate chamber with cathode, grid and plate elements,and whereof

